Light-emitting device with a sealing integrated driver circuit

ABSTRACT

The invention relates to light-emitting diodes (O-LED). In particular, it relates to the driver electronics needed for these devices. An organic electroluminescent device is provided, which has a hermetically closed very flat housing. To improve the functionality of an O-LED, considerably reduce the height of an O-LED module and allow a cost-effective mass production, the driver circuit and the electronic driver elements or the printed circuit board (PCH) with the electronic driver elements are incorporated into the cover plate of the device.

The invention relates to an electroluminescent, e.g. a light-emittingdevice (O-LED) with a sealing integrated driver circuit. In particular,it relates to the driver electronics needed for this device. Such adevice comprises a transparent substrate and a cover plate having afirst side facing the transparent substrate and a second side oppositethe first side, at least one electroluminescent element comprising anorganic electroluminescent layer arranged between the transparentsubstrate and the cover plate, and an intermediate sealing means joiningthe transparent substrate and the cover plate.

Organic light-emitting diodes (O-LED) are a high-potential solution forfuture light sources. They are expected to become a high-efficiencylight source in a wide area for cost-effective manufacture. However,they typically need driving electronics to adapt the available supplyvoltage to the required current of the O-LED. In order to achieve a highefficiency of the whole system, these driving electronics should beswitched-mode power supplies with various types of electroniccomponents. In order to integrate this circuit, a printed circuit board(PCB) mounted on the rear side of the O-LED can be used, so that a tightand flat construction is obtained.

Such a device is disclosed in WO 03/034513. The intermediate sealingmeans of the device is used as the substrate for the drivingelectronics. The problem is that the conventional components needed forthese electronics are typically bulky and stiff elements. This is incontrast to the thin and, if possible, flexible O-LED elements. Thedevices described in WO 03/034513 are based on a substrate layer made ofglass and a circuit board made of ceramics.

It is therefore an object of the invention to provide an organicelectroluminescent device of the type mentioned in the openingparagraph, which is provided with a hermetically closed very flathousing. Moreover, it should improve the functionality of an O-LED,considerably reduce the height of an O-LED module and allowcost-effective mass production.

This object is realized in that the driver circuit and the electronicdriver elements or the printed circuit board (PCB) with the electronicdriver elements are incorporated into the cover plate of the device.

Consequently, all driver components can be arranged together with theO-LED in a construction which is as flat as possible. As a result, thedevice is much flatter than that cited in the state of the art.

In the functional result of the invention, the technical fact that anO-LED is naturally flexible in itself is used to distinguish thisfeature by constructing a circuit board which is just as flexible as theO-LED. The complete device thus finally remains flexible, which is agreat advantage in a large number of possible technical applications.This combination of a flat construction and great flexibility results ina very flat and effective device.

A further advantage of the invention is that a lamp covering a largearea consists of a number of cells. The invention allows equipping eachcell with its own driver on the rear side. In this way, each cell may beeasily controlled in order to achieve a homogeneous light output of allcells or the application of certain light patterns. Various electronicfunctionalities are possible, which can be integrated in the back of anO-LED by using this inventive compact, yet flexible construction.

Due to the provision of the driver device, a very simple supply may be aseries resistor which can be integrated in the circuit board to adjustthe device, e.g. the diode current to the supply voltage. This resistormay be chosen from another flexible material.

A somewhat more advanced solution may be a linear control circuit, whichis e.g. realized with a current-controlled transistor. Since thistransistor does not need to be fast, printed polymer transistors canalso be used, so that the construction remains both flat and flexible.

The driving electronics preferably consist of a DC/DC converter. Astep-down converter with current control is applied for a supply voltagewhich is higher than the diode voltage of the O-LED. A step-up converterwith current control is applied for a supply voltage which is lower thanthe diode voltage. A flyback converter with an integrated transformermay also be used for a large difference between supply voltage and diodevoltage. The secondary side diode of the flyback can be omitted and theO-LED can be used for this purpose. Each converter is equipped with acontrol stage, such that the output of each cell can be controlledindividually. This is important for generating light patterns usinginvention-related O-LEDs.

Also coils, which are flat and flexible, can be produced andincorporated into the device. These coils are needed for severalapplications. The coils serve for the remote powering of the O-LED (awireless powered O-LED). This combination is very effective becauseflexible O-LEDs for generating light patterns can be obtained, whichO-LEDs are as flat as films, because no external-to-internal connectionof conducting paths is necessary.

It is possible to integrate further electronic elements such as WIFI forremote communication between O-LED systems and/or passive filtersconsisting of LC combinations in order to filter disturbances, and alsopassive narrow-band filters consisting of LC-combinations (e.g. a seriesresonator), wherein each filter selects a certain frequency withoutreducing the flexibility of the complete device.

Different O-LED cells are provided with filters of different centerfrequencies. Each cell may then be controlled by its related frequency.Groups of cells may have the same frequency, e.g. all red cells, allgreen cells, and all blue cells have the same frequency. The RGB-colorof all cells can thus be jointly controlled.

Each cell may be equipped with a tiny transformer integrated in the PCBto adapt an AC-bus voltage to the cell current. The secondary side ofthe transformer may be equipped with an additional rectifier stage (e.g.full bridge, half bridge, or single diode rectifier). Alternatively, twoneighboring cells can be connected in an anti-parallel way, thus workingas a rectifier. In this way, no additional external rectifier isnecessary.

The primary side of the transformer can be distributed across a largearea covering a number of cells. In every cell, a secondary windingpicks up a part of the magnetic flux to drive the cell. In this way, nointerconnections to each individual cell are necessary.

Integrated capacitors may act as analog sample-and-hold devices to alloweasy multiplexing of a large number of cells.

Intelligence is added to the driver for stand-alone operation of eachcell, e.g. for setting individual light patterns or color schemes.

As a solution, the printed circuit board (PCB) on the rear side containsintegrated, planar components. This can be realized either as anassembly or as a fully integrated O-LED device in which the rear side ismade of a printed circuit board. In this way, the sealing of the O-LEDeven performs an electronic function. A further Figure shows an examplewith an integrated inductor. The aspect ratio in the Figures is not 1:1,but the thickness of the printed circuit board (PCB) is exaggerated.Also further passive components such as capacitors or resistors can beintegrated in the PCB.

All of these combinations of features with the features defined in theindependent claim open up an immense field of application ofinvention-related O-LEDs which are flat and flexible or bendable. In theinvention, polymer materials are used by way of example for printedcircuit boards. As compared with the state of the art, it is anadvantage that this type of material is less expensive and is availablein larger sizes than ceramic materials. By using a flexible printedcircuit board material such as polyimide, also flexible components canbe integrated in this flexible substrate, which even comprisesinductors.

In this way, the sealing and the electronics can be made flexible, sothat a completely flexible or bendable display module can be obtained.

It is also advantageous that, in one explicit solution, each cell orgroup of cells is equipped with electronic bus-address units, by whicheach luminescent element or cell or group of luminescent elements orcells can be identified and selectively generated. Each cell or group ofcells can thus be generated selectively, and no conductive paths arenecessary in combination with a contactless inductive intercoupling.

In the context of the invention, the electronic elements for thebus-address units are also implemented and incorporated into the coverplate in the way described. In a particular combination, thisbus-address circuit is also constructed with planar components only,and, in a special solution, such a device is flexible or bendable.

It is thus possible to create semiconductor elements in such a thinconstruction that they are flexible or bendable. This can be realizedwith classical anorganic semiconductors as well. Dimensions of thicknessmust be less than 100 micrometers.

These and other aspects of the invention are apparent from and will beelucidated with reference to the embodiments described hereinafter.

In the drawings:

FIG. 1 shows an O-LED with a flex foil as top sealing.

FIG. 2 shows an O-LED with a flex foil as top sealing with a substratefor driver electronics.

FIG. 3 shows an O-LED with an integrated inductor.

FIG. 1 is a cross-sectional view of an O-LED 20 with a flexible foil astop sealing 10 and interconnection. The complete structure is layered,rendering it flexible and bendable.

The transparent substrate 1 on the light-emitting side of the O-LED 20is a light-transmitting flexible material in the sense of the disclosedinvention. The flex foil 10 is a layer with a polyimide core with copperlayers 2 on both sides in order to realize an interconnection betweenthe inner O-LED and the outer conducting paths. Therefore, this flexfoil is bendable.

The O-LED cells 3 are located between the flex foil 10 and thetransparent substrate 1. The O-LED cells themselves consist of aconducting layer 4 on one side and a transparent conducting layer 5 onthe other side which faces the transparent substrate 1. The active O-LEDlayer is located between the conducting layer 4 of the O-LED cell andthe transparent conducting layer 5 of the O-LED.

The transparent conducting layers of several O-LED cells can be kepttogether, but the conducting layers on the other side of the O-LEDs mustbe separated, i.e. they have to be isolated from each other in order toactivate each O-LED itself, i.e. independently of each other.

The gap between the transparent substrate and the flex foil is sealedwith a side sealing 8 at least at the outer sides of an O-LED.

The conducting layers of the O-LEDs are bonded with conducting posts,which interconnect these conducting rear sides of the O-LEDs with theinner conducting layers, in this case copper layers 2 of the flex foil10.

The O-LED-cells 3 are preferably positioned on the transparent substrate1, or, more preferably, on the transparent conducting layer 5 with adefined gap between each other.

The conducting posts 7 for the common transparent conducting layer islocated in this gap. The dimensions of the conducting posts 7 and thegaps are combined so as to preclude a shortcut between these conductingposts and the conducting layers of the O-LED cells.

In this respect, it should be considered that no shortcut in the sensedescribed can take place in the range of the predetermined maximalbending or flexing action.

Through the polyimide core 9 of the flex foil 10, there is a conductivevia 6 between the conductive layer inside and the conductive layeroutside.

FIG. 2 is a cross-sectional view similar to that in FIG. 1. An O-LED 20is shown with flex foil 10 as a top sealing with substrate for driverelectronics 11. The multilayer sandwich construction is similar as inFIG. 1, but the flex foil 10 is a multilayer system with two polyimidecores 9, the first of which has substantially the same construction asin FIG. 1, but the second flex foil layer has an integral circuit boardfor the driver electronics 11. One possibility for construction is tomount the electronic components 11 on top of this circuit board which isan integral part of the top sealing of the complete device.

Another possibility is to position at least some electronic componentsin the intermediate layers of the top sealing. In both constructionalternatives, the complete device is flexible and bendable and it isnecessary to consider the desired range of flexibility so that asatisfactory contact with all electronic components is realized in everycase.

In this sandwich construction of the top sealing, the external topsurface carries the conductive paths, which may be made of copper layers2, as is customary for printed circuit boards. Interconnections fromthese layers to the inner layer of the top sealing downwards arerealized by conducting vias 6, which are made of copper in this case.

FIG. 3 is a cross-sectional view of an O-LED with an integral inductor30 which is completely incorporated into the top sealing of this device.In this embodiment, a sandwich construction similar to that in FIG. 2 isshown. The intermediate layer bulk comprises an inductor 30 consistingof a soft magnetic core 31 and a spiral winding 32. These inductorcomponents 31, 32 are completely integrated, i.e. they are completelyincorporated into the bulk of the upper layer of the flex foil 10.

Also in this alternative, the flex foil 10 remains flexible andbendable. The spiral winding 32 as well as the soft magnetic cores 31are therefore created in a thin-layered way. The rest of theconstruction is similar to that shown in FIG. 2.

The integrated inductor couples with an external inductor. This resultsin a contactless steering of the O-LED.

Similarly as with inductors, it is possible to integrate capacitors inthe sealing top, i.e. the flex foil. This may enable devices to alloweasy multiplexing of a large number of cells.

As defined in the claims, the invention leads to a very compact, i.e.flat construction of the O-LED. Furthermore, the flat constructionsupports the option to create the O-LED in a flexible and bendable way.This special embodiment will generate really new fields of applicationof O-LEDs.

1. An electroluminescent device with a sealing integrated drivercircuit, the device comprising a transparent substrate, a cover platehaving a first side facing the transparent substrate and a second sideopposite the first side, at least one electroluminescent elementcomprising an organic electroluminescent layer arranged between thetransparent substrate and the cover plate, an intermediate sealing meansjoining the transparent substrate and the cover plate, and a printedcircuit board (PCB) having a plurality of electronic driver elementsdisposed thereon, wherein the printed circuit board is incorporated intothe cover plate, and at least one of the driver elements comprisesprinted polymer semiconductor material.
 2. A device as claimed in claim1, wherein the plurality of driver elements comprises a series resistorcomprising a flexible, electrically resistive material integrated in theprinted circuit board.
 3. A device as claimed in claim 1 , wherein theplurality of driver elements comprises a linear control circuitincluding a current-controlled transistor.
 4. A device as claimed inclaim 1, wherein different electroluminescent elements are provided withfilters of different center frequencies in order to group differentcells to an assembly with different light colors.
 5. A device as claimedin claim 1, wherein, in an assembly or an arrangement of severalelectroluminescent elements or cells, each element or cell is equippedwith a transformer integrated in the PCB in order to adapt an AC-busvoltage to the cell current, wherein the second side of the transformeris equipped with a rectifier stage.
 6. A device as claimed in claim 1,wherein each cell or group of cells is equipped with electronic busaddress units for identifying each luminescent element or group ofluminescent elements.
 7. A device as claimed in claim 1, wherein thesemiconductor elements are bendable or flexible.
 8. A device as claimedin claim 1, wherein the transparent substrate and the cover platecomprise a flexible or bendable material.
 9. A device as claimed inclaim 8, wherein the plurality of driver elements comprises a DC/DCconverter including a control stage, such that the output of the atleast one electroluminescent element is individually controllable inorder to generate light patterns.
 10. A device as claimed in claim 1,wherein at least one coil for remote powering of the at least oneelectroluminescent element is incorporated into the cover plate.
 11. Adevice as claimed in claim 10, wherein the electroluminescent element isan organic light-emitting diode O-LED.